With no inspection or acceptance marks,(That I can see) and the cock and frizzen being a bit "off", and the tumbler not being an EIC type, I think it was maybe re-built on the sub-continent or altogether locally made.
The date also sounds a bit ominous, as it isn't a 1757 lock, and in 1857 the EIC was using percussion arms and had been for some time.
Also 1857 was the year of the Mutiny....
Sorry if this sounds a bit unwelcome!

The first photo shows the style of lock marking used until 1804. The date was apparently not engraved on the lock before 1775.
Between 1804 and 1807 the heart and date appeared in the centre of the lock and the maker's name across the tail.

Second picture;

This photo shows the style of lock marking used between 1808 and 1818. There are several different lion stamps in evidence, some being rather crude and cartoon-like.

Third photo,
Here are the markings on a Baker Pattern lock 1819 to 1839. This late production example has the date code C for 1839. This lock also features the "bun nut" securing the cock to the tumbler.